1. Field of the Invention
This invention relates to a disc cartridge, and more particularly to a disc cartridge for a hard disc, a floppy disc, a magnetic disc, a magneto-optical disc or the like.
2. Description of Related Art
Conventionally, a disc cartridge such as a floppy disc cartridge, a magneto-optical disc cartridge or the like has been well known in the art. Such a disc cartridge is divided into several types such as an MFD type having a single central shaft and a single drive shaft, a VFD type having a central shaft provided with a spring, an optical disc type having only a central shaft, and the like. These types are common in that a disc is provided at a central portion thereof with a hub which is formed with a drive shaft inserting hole adapted to engaged with a drive unit.
The conventional MFD type disc cartridge includes only one drive shaft; therefore, application of any external force thereto causes a variation of centering force during one revolution of a disc to be increased, so that it is required to manufacture a hub and a driving unit with high dimensional precision, leading to an increase in manufacturing cost. Also, it fails to exhibit satisfactory reliability. Further, it causes centering force to be negative during one revolution of the disc when frictional force is increased due to any change of a medium with time, to thereby generate eccentricity sufficient to cause a failure in modulation, and resulting in deteriorating its value as a commercial product.
The conventional VFD type disc cartridge is so constructed that a hub is formed of a plurality of parts. Such construction causes the cartridge to be complicated in both structure and manufacturing, leading to an increase in cost. Also, in any optical disc type cartridge, only centering between the central shaft and a shaft inserting hole is carried out, so that it is required to manufacture a hub and the shaft with high dimensional precision. This likewise causes manufacturing of the cartridge to be complicated and troublesome sufficient to lead to an increase in cost.